Portable electronic devices such as personal digital assistants (PDAs), cell phones, digital cameras, MP3 players, and laptop computers often use a type of infrared transceiver called an IrDA (Infrared Data Association) transceiver to transfer information. Each IrDA transceiver has an infrared light emitting diode (LED) that emits infrared radiation having a center wavelength somewhere in the range of from 850 nm to 900 nm (for example, 875 nm). Each IrDA transceiver also has an IR receiver (for example, a PIN diode) for receiving infrared signals of this wavelength. If, for example, each of two such portable electronic devices has an IrDA transceiver, then one device can transmit data to the other device across an IrDA link using infrared signals that comply with an IrDA standard. IrDA is, for example, often employed to communicate files of digital information between portable devices having such IrDA transceivers.
Electronic consumer devices in the home such as televisions, VCRs, DVD players, DVRs, CD players, stereo equipment, home theatre equipment, and so forth are typically controlled by remote control (RC) devices that also transmit infrared signals. These ordinary infrared signals, referred to here as “RC” (or remote control) infrared signals, typically have a center wavelength somewhere in the range of from 900 nm to 950 nm (for example, 940 nm). To turn the power on to a television, for example, a user may press a power key on a remote control device. The remote control device has an infrared LED that emits an RC infrared signal to the television. An infrared RC receiver circuit in the television receives the RC infrared signal, decodes the signal, and responds by turning the television on.
It has been recognized that it would be desirable to be able to use a portable electronic device to control an electronic consumer device that is designed to respond to RC infrared signals. If, for example, a user had a cellular telephone in his/her hand, then the user could use the cellular telephone to control a television.
It has been recognized that an IrDA transmitter LED within an IrDA transceiver module can be used as an infrared transmitter both for IrDA and RC applications. Although the peak wavelength of the transmitter LED in the IrDA transceiver is at a wavelength that is different from the wavelength of peak sensitivity of the RC infrared receiver in the electronic consumer device, some radiation transmitted by the infrared transmitter is nevertheless received by the RC receiver. The IrDA transmitter transmits energy in a band and the RC receiver receives energy in a band. The two bands overlap. Due to the mismatch of the center transmitter and receiver wavelengths, however, it may be necessary for the IrDA transmitter LED power to be increased in order for enough energy to be received at the RC receiver for the communication to work properly. An application note from Vishay Semiconductors (Vishay Semiconductor Application Note entitled “Utilizing a Vishay IrDA Transceiver for Remote Control”, document number 82606, 14 pages, Feb. 20, 2004) discloses reducing the value of a current-limiting resistor so as to increase IrDA LED transmitter peak current and thereby to increase emission intensity of the IrDA LED transmitter.
Improvements and enhancements to a system employing an IrDA transceiver to transmit infrared signals to an RC receiver are sought.